1. Field of the Invention
The present invention relates to medical apparatus and methods and more particularly to electroconvulsive therapy (ECT) apparatus and methods for automatic monitoring of the duration of patient seizures.
2. Description of the Related Art
In electroconvulsive therapy (ECT) generally two electrodes are applied to the temple of the patient, one on the left and the other on the right side, and a small and carefully controlled electric current is applied for less than ten seconds between the two electrodes. Only a small portion of the current reaches the brain because most is deflected by the skull.
Electroconvulsive therapy ("ECT") may be used to treat major depression. A report of a NIMH panel (National Institute of Mental Health), reported in Science (Jun. 28, 1985, pgs. 1510,1511), concluded that "not a single controlled study has shown another form of treatment to be superior to ECT in the short-term management of severe depressions." That article stated that the complication rate is about 1 in 1700 treatments and that severe and prolonged memory loss is extremely rare, and possibly non-existent.
In ECT, the physician determines the length of the applied current, taking into account such factors as the patient's age, size, physical condition and prior ECT. The physician may, with presently available apparatus, reasonably accurately select the desired electrical duration. For example, in the "Thymatron" ECT instrument (TM of Somatics, Inc., Lake Bluff, Illinois) the stimulus may be selected to be a brief series of electrical square waves, providing a constant current of 0.9 amps limited to 450 volts, consisting of 140 bipolar pulses per second of 1 msec width, which is adjustable, by the physician, 0.2-4.0 seconds in duration.
ECT induces an electrical response in the neural tissue of the patient's brain and its therapeutic benefit is primarily due to the induced seizure. That seizure may be displayed on an electroencephalograph (EEG) instrument, using analog printed wavy lines. It presents a pattern similar to a typical epileptic grand mal seizure pattern.
When administering ECT, the physician may monitor the patient to determine the occurrence and duration of the induced seizure (American Psychiatric Association Task Force on ECT Report, Washington, D.C. 1990, pp. 28-29). An electrical stimulus that does not induce a seizure, or induces a seizure of insufficient duration (e.g., less than 20 seconds) is not considered to have sufficient therapeutic effect. If a seizure of sufficient duration is not induced, the treatment may be repeated with a larger electrical dosage, i.e., generally a greater electrical charge, to try to induce a suitable seizure.
In electroconvulsive therapy (ECT) it is desirable that each treatment appears to achieve a definite therapeutic impact. The criteria for apparent effectiveness of the treatment is that muscle (motor) manifestations of the seizure of ECT last for at least 20 seconds and appear generalized through the body. If the seizure is shorter, or the seizure is local rather than generalized, the treatment should generally be repeated, usually with a larger electrical stimulus. A seizure that is unduly long (e.g., longer than 3 or 4 minutes) may cause excessive memory impairment in the patient, or interfere with the patient's orientation to the environment, or require more intensive supervision of the patient during and after the treatment. It is accepted medical practice to immediately terminate such prolonged seizures by administration of suitable intravenous anticonvulsant agents according to the physician's judgment.
Generally, the conventional methods which monitor the electrical activity of the brain during ECT are based on analog EEG technology. For example, an EEG device amplifies the patient's brain waves, filters the amplified brain wave signals to remove muscle artifact and ambient electrical noise, displays the brain wave activity in the form of wavy lines on paper or lines on an oscilloscope screen, or produces similarly fluctuating audible tones played through an audible speaker. The physician determines the occurrence of the seizure by viewing the paper EEG record, oscilloscope display, or hearing the auditory EEG signal. He determines the length of the seizure by interpreting the particular representation of the EEG signal (a spike-like form on an EEG graph) while simultaneously viewing a timepiece. However, the physician's interpretations of the visual, or auditory, EEG signals require familiarity with EEG patterns that occur during ECT. That interpretation is subjective, relies on the attention and experience of the physician, and has been reported in the medical literature to be unreliable (Ries, R. K., Biol. Psychiat. 20:94-119, 1985). The physician, to determine the duration of the seizure, must pay attention to the visual, or auditory, representation of the EEG signal, as well as to a separate timepiece, at the same time his attention is required to observe the patient undergoing the seizure.
In the inventors' U.S. Pat. Nos. 4,873,981 and 4,878,498, incorporated by reference herein, the duration of the patient's seizure is automatically monitored. The patient's brain wave activity is amplified by an EEG system, converted to digital data, and compared to the patient's own reference value to determine when a selected EEG parameter has crossed the predetermined reference value ("crossover") and the time which has elapsed from the termination of ECT until the crossover.
It has also been suggested that as an alternative, or as an addition, to the EEG, the patient's muscle activity may be monitored by the physician to determine the end of the seizure, since such ECT-induced seizures provide characteristic involuntary muscle activity. However, generally prior to the ECT the patient will be partly or wholly anesthesized or treated with muscle relaxing pharmacologic agents to obtain anesthesia and prevent bone and muscle injury. Consequently, the patient's muscle activity may be so repressed as to be an unreliable indication of the termination of the seizure. One suggestion, to avoid this problem, is to isolate the monitored muscle group from the muscle relaxing drugs by applying a tourniquet and then for the physician to observe the muscle activity, i.e., a "cuffed limb", see Greenberg, "Detection of prolonged seizures during electroconvulsive therapy; a comparison of electroencephalogram and cuff monitoring", Convulsive Therapy, 1:32-37, 1985. However, that method has not been widely adapted, possibly because it requires that physician's attention during a critical period of the ECT. In addition, although seizure-associated muscle activity can be reliably observed by occluding arterial flow to a limb prior to infusion of the muscle paralyzing medication, in many cases seizure activity observable on the EEG has continued long after cessation of observable muscle activity with this "cuffed-limb" method. The "cuffed limb" method cannot describe the quality of generalization of the seizure over the patient's body, because its observation is made only on one limb. It also absorbs staff time, and is unsuitable for patients who are susceptible to osteoporotic bone fractures.
Another alternative or addition to the EEG is the duration of elevation of the heart-beat rate. Such elevation reliably accompanies the seizure activity. The heart-beat rate declines abruptly at the end of the seizure, and the point of greatest descent of this rate consistently marks the end of the seizure.
Generalization of muscle seizure activity over the body does not imply generalization of electrical seizure activity through the brain, which is the goal, because control of muscle activity concerns only a small fraction of the brain. Observation of the EEG, EMG and ECG together describes generalization of electrical seizure activity through the brain. This is because the EEG represents activity in the prefrontal cortex of the brain, the EMG represents activity in the motor area of the brain slightly forward of the middle, and ECG heart rate represents activity in the lower brainstem, which is entirely across the brain from the prefrontal cortex.